1. Field of the Invention
The invention relates generally to switch points for railroad tracks and, more particularly, to means for positively determining the position of such switch points.
2. Description of the Prior Art
Railway turnouts alternatively divert trains from one track to other tracks. A common turnout used in the industry has a switch property which includes switch points, a switch machine and an operating rod to initiate diversion of the wheels, a frog to carry the train wheel flanges across opposing rails and lead rails between the frog and the switch. The switch points are typically moved by means of the operating rod which is attached to the switch point and is also connected to the switch machine. In operation, the operating rod is translated by the switch machine causing the switch points to move.
A switch circuit controller is a device that is mounted to the railroad ties and is connected to the operating rod. The switch circuit controller provides a signal indicating the position of the switch point. The signal produced by the switch circuit controller is a vital indication which means that the signal need not be checked further and may be presumed to be accurate. A typical switch circuit controller of the prior art is the U-5 switch circuit controller manufactured by Union Switch & Signal Inc. which is shown in prior art FIGS. 1 and 2.
As an alternative to a single operating rod that is connected to the switch circuit controller, one or more switch rods that are separate from the operating rod may be connected to the switch point, and the switch circuit controller may then be connected to this switch rod. As the switch point moves back and forth, the switch rod which is connected to the switch point will also move back and forth.
Whether the switch circuit controller is connected to the operating rod or to a switch rod, movement of the rod will cause a crank arm (depicted as "a" in prior art FIGS. 1 and 2) of the switch circuit controller to rotate. The switch circuit controller typically has a cast iron housing (depicted as "b" in prior art FIGS. 1 and 2) having circular openings through opposed side walls. The crank arm is located outside of the controller housing and is connected to a cam shaft. The cam shaft (depicted as "c") is rotatable, having one or more cam segments (depicted as "d") provided thereon. The cams are sized, configured and positioned so as to be engageable with one or more movable followers (depicted as "e"). The followers are spring-biased toward a given position. The followers further are connected to respective movable electrical heel contacts (depicted as "f").
The switch circuit controller also has a contact spring assembly that is comprised of two spaced-apart fixed electrical contacts (called front and back contact springs and depicted as "g" and "h", respectively) and the movable heel contact. The heel contact spring is positioned between the front contact spring and the back contact spring and may alternatively make contact with either the front or back contact spring. Silver pads are provided on the heel contacts and silver tips are provided on the distal ends of the front and back contacts to increase conductivity through the contacts.
The contact spring assembly is mounted within the switch circuit controller by being secured to a terminal board (depicted as "i"). The terminal board is in turn mounted within the switch circuit controller housing. The housing b is equipped with integrally cast vertical ribs j. Terminal board i abuts the as-cast surfaces of ribs j and is retained by them by brackets k and bolts l. The terminal board is made of an insulative material. Thus, the terminal board performs the function of supporting the contact spring assembly and also performs the function of insulating the contact springs from one another and the metal housing.
When the operating rod is thrown by the switch machine to move the switch point, the translation of the operating rod causes the crank arm to rotate. When the crank arm rotates, the cam shaft rotates within the switch circuit housing. The cams attached to the cam shaft then engage the followers. The followers are normally spring-biased so that the movable contacts to which they are connected are biased into contact with the back contact springs. When the cams engage the followers, the movable contact springs are forced forward into contact with the front contact springs. Contact of the movable contact springs with either the front contact springs or the back contact springs causes different circuits to be completed, which in turn causes respective signals to be produced. Thus, movement of the switch point causes electrical contacts to be made inside the case of the controller.
The terminal board of the prior art is typically made of a thermoset phenolic plastic such as Bakelite manufactured by Union Carbide Corp. Two ribs are then cast integral with the housing of the switch circuit controller. The terminal board is drawn up against the ribs and tightened down thereto by means of a bracket or a number of brackets, and mounting bolts. The brackets are mounted to the terminal board and are so configured that tightening a threaded fastener upon them will force the terminal board onto the ribs. The mounting bolts pass through aligned holes in the terminal board and the ribs.
The lost motion between the cams of the cam shaft, the crank arm and the operating rod often must be adjusted. Further, adjustments must be made between the movable contact springs and the front and back contact springs. Such adjustments are often difficult because the as-cast housing of the switch circuit controller may have slight deviations in the ribs. Furthermore, the locations of the front and back contact springs, relative to the can shaft, depends upon the location of the ribs relative to the openings in the controller housing through which the cam shaft is disposed. If the ribs are not cast the correct distance from the location of the openings in the housing for the cam shaft, difficulty is encountered when an attempt is made to adjust the contact springs. Also, excessive roughness of the sand cast surfaces of the ribs will not allow the terminal board to sit securely. Because of the location and configuration of the ribs, machining the ribs to provide a smooth mounting surface for the terminal board is difficult.
Therefore, a switch circuit controller that has means for positively locating the terminal board is needed. Such means should simplify the manner in which the terminal board is mounted to the controller housing, while providing adequate support of the contact spring assembly.